He may not be famous for it but it has been noted many times that the Donald does not laugh. He just never lets out an unimpeded round of laughter. His facial expression varies in a narrow range between a neutral gaze and a grumpy scowl. He can’t express enthusiasm, just intensity.
Obviously he is totally lacking in self-awareness, otherwise he would be terribly embarrassed by his juvenile utterances. But he is not in the least embarrassed by his nonsensicalness both verbal and tweeted, and that trick would be difficult to fake had he the least bit of normal human self-awareness. He is like an innocent child who can say things with a straight face that an adult would never seriously speak.
And of course the why of Trump keeps circling back to the relentless ego of Trump. It is as if all reason and emotion with him is trapped inside a cage of brittle ego, something that he is terrified might break, exposing him helpless before the world. And that friends is no laughing matter, right Donald?